The present invention relates to a flow path switching apparatus capable of effectively forming a fluid flow path in an automatic regulating valve such as a steam trap or a pressure reducing valve.
When a steam trap is generally installed in a pipe, as shown in FIG. 11, a pair of stop valves 101 and 102, a strainer 103, and an automatic regulating valve 104 are arranged in a pipe 105. A bypass pipe 108 having a stop valve 107 is connected in parallel with the pipe 105. With this arrangement, the strainer 103 and the automatic regulating valve 104 can be inspected, adjusted, replaced, and the like by the above piping technique. Every time inspection or the like is to be performed, the valves 101, 102, and 107 must be independently controlled, resulting in cumbersome operations. Even if an automatic control valve 110 incorporating a strainer shown in FIG. 12 is used, a piping network can be slightly simplified.
To the contrary, a steam trap apparatus described in Japanese Utility Model Laid-Open No. 63-57897 is effective to simplify the piping network. As shown in FIG. 13, a cylindrical switching valve plug 128 is fitted in a valve cage 120 having a fluid inlet 121 and a fluid outlet 122 which constitute an almost U-shaped flow path. The cylindrical switching valve plug 128 has a pair of valve holes 124 and 125 which can be connected to the fluid inlet 121 and the fluid outlet 122, and a bypass path 126 for causing the fluid inlet 121 and outlet 122 to communicate with each other. A steam trap portion 130 is connected to a portion of the valve cage 120 at a position opposite to the fluid inlet 121 and the fluid outlet 122. Upon pivotal movement of the switching valve plug 128, a flow path communicating with the stream trap portion 130 through the valve holes 124 and 125, a flow path constituted by the bypass path 126, or a state in which the fluid inlet 121 communicates with the fluid outlet 122 is selectively obtained. As a result, the bypass pipe and the stop valve which are required for inspection of the steam trap portion 130 can be omitted, and the resultant piping structure can be simplified, as shown in FIG. 14 (see FIGS. 11 and 12).
In the above steam trap apparatus, a total of four teflon flat packings must be arranged at the connecting portions between the valve holes of the switching valve plug and the fluid inlet and outlet as well as the connecting portions between the valve holes of the switching valve plug and the steam trap portion. In addition, when the valve plug is pivoted to align the valve holes 124 and 125 with the fluid inlet 121 and the like, leakage of the steam into the valve chamber cannot be prevented while the opening ends of the valve holes cross the surfaces of the packings 131, thus requiring a ground packing 132. Leakage is caused by end deformation of the packing itself, and it is difficult to perfectly fit the packing along the inner surface of the valve chamber due to flatness of the packing. As a result, a perfect sealing effect cannot be obtained, thus posing a decisive drawback of the apparatus of this type. As is apparent from FIG. 14, the conventional steam trap apparatus has a so-called U-turn type piping structure. In other words, a linear piping path cannot be formed, and the piping space cannot be effectively reduced. In addition, the switching valve plug portion becomes bulky as compared with the steam trap portion. Furthermore, since the axes of the valve chamber portion and the steam trap portion are different (XX axis and X'X' axis), chucking must be independently performed during machining, thus posing many problems due to a complicated structure. When the automatic regulating valve (A) incorporating the strainer shown in FIG. 12 is used, the position of the strainer is fixed after installation. When the automatic regulating valve is located near a wall of a building or other facilities, it is very difficult to remove the strainer.